1. Field of the Invention
The present invention relates to a cam mechanism which includes a cam ring on which at least one cam rib is formed and which can be used in a lens barrel, e.g., a photographing lens of a camera. More specifically, the present invention relates to a cam rib support structure which supports each cam rib by an associated pair of cam followers formed on a follower ring which is provided concentrically with the cam ring.
2. Description of the Related Art
A cam mechanism including a cam ring and a follower ring which are concentrically arranged, wherein at least one cam rib extending non-linearly is formed on an inner or outer peripheral surface of the cam ring while a corresponding at least one pair of cam followers are formed on an outer or inner peripheral surface of the follower ring, is known in the art. This type of cam mechanism will be hereinafter referred to as “cam-rib-incorporated cam mechanism”. The present invention relates to a support structure of the cam-rib incorporated cam mechanism which supports each cam rib by an associated pair of cam followers therebetween which are formed on the follower ring. This type of support structure will be hereinafter referred to as “cam rib support structure.” In the cam rib support structure, if the primary cam diagram of the cam rib has only a circumferential component (i.e., if the primary cam diagram extends only in a circumferential direction of the cam ring), the pair of cam followers must be positioned apart from each other in the axial direction of the follower ring to hold the associated cam rib between the pair of cam followers. In other words, a pair of cam followers cannot hold the associated cam rib therebetween if positioned apart from each other only in a circumferential direction of the follower ring. The follower ring is usually guided linearly along the optical axis without rotating. Accordingly, rotating the cam ring forward and reverse causes the follower ring to move forward and rearward in the axial direction thereof.
In the cam rib support structure, during assembly thereof, one of the cam ring and the follower ring is inserted into the other so that that each cam rib is positioned between the associated pair of cam followers. In this assembly operation, one of the cam ring and the follower ring must be rotated relative to the other in a state where one of the opposite ends (insertion end) of each cam rib in the lengthwise direction thereof is positioned in between the associated pair of cam followers in the axial direction of the cam ring and the follower ring. However, the axial position of each pair of cam followers on the follower ring cannot be visually identified from the outside of the follower ring because one of the cam ring and the follower ring is positioned around the other. Accordingly, a special assembly jig or skill is conventionally required to assemble the cam ring and the follower ring together. This makes the process of assembling the cam ring and the follower ring difficult.